1. Field of the Invention
This invention relates to an on-vehicle fuel property detection device, among members including a fuel supply apparatus, which is mounted in a fuel tank of a vehicle or the like, and which pressurizes and supplies fuel to an injector that injects fuel into an engine. Specifically, this invention relates to the detection device using an optical fiber.
2. Description of the Related Art
Recently, alcohol-blended fuel mixed with bioethanol has become widely used at an accelerated rate as an alternative to gasoline. However, in such alcohol-blended fuel, an optimum ignition timing, an optimum air-fuel ratio and the like vary with a concentration of ethanol contained in the fuel. Thus, in order to achieve appropriate engine control by a computer, i.e., an electronic control unit (ECU), it is necessary to accurately detect the concentration of alcohol contained in the fuel.
It is known, as one of means therefor, to detect the property of a liquid by an optical fiber sensor having an optical fiber, a light source and a light receiving portion (see, e.g., WO2006/126468 (Embodiment 20)). The optical fiber includes of a core having an area in which a grating is formed and a clad. The optical fiber is disposed at a position at which at least a part of the area in which the grating is formed is immersed in the liquid. The light source outputs light, whose wavelength is within a band of wavelengths of light corresponding to a cladding mode to be caused due to the grating of the area in which the grating is formed, to be incident on the optical fiber. The light receiving portion detects the intensity of light which is incident on the optical fiber from the light source and transmitted by the grating of the area.
WO2006/126468 discloses that the property of fuel stored in a fuel tank is accurately detected by providing an optical fiber probe in the fuel tank (in the case of Embodiment 20) or outside the fuel tank (in the case of Embodiment 19). Between these cases, the case of providing the optical sensor probe in the fuel tank as in Embodiment 20 has an advantage in that the detected property is insusceptible to temperature and heat, as compared with the case of providing the optical sensor probe outside the fuel tank, more particularly, in the vicinity of a vehicular engine room. However, on the other hand, the optical fiber used in the optical sensor probe described in WO2006/126468 is bent like a letter “U” regardless of which of the transmission type and the reflection type the optical fiber sensor is. The influence of the bending of the optical fiber superimposes on the properties of the fuel. Consequently, the optical fiber sensor described in WO2006/126468 has a problem of increasing an error of the detected properties.